This invention relates to circuitry for programming a programmable read-only memory (PROM) and more particularly to a combined programming circuitry for programming such a memory and for reading the information contained in said memory.
Matrix arrays in which information is permanently located are known in the art. The matrix array, as a single integrated circuit, comprises rows and columns of parallel electrical conductors formed with the devices connecting the intersections or cross-over points of the rows and columns. After the manufacture of the matrix, the connecting devices at predetermined intersections of the rows and columns are permanently altered by the application of a current pulse across the connecting device to render the connection between intersection inoperative thus forming a read-only memory (ROM). The connecting device is either opened or closed depending on how the PROM is programmed.
There are a number of patents such as the U. S. Pat. to Rizzi et al No.'s 3,742,592, 3,848,238, and 3,733,690 and the U.S. Pat. to Castrucci No. 3,641,516 showing matrix arrays with connecting devices at the intersection of the rows and columns and showing methods of applying suitable current to the selected conductors to program the memory.
This invention is directed to circuitry for programming the memory matrix in which current for selecting a memory row is handled by a minimum number of active components and thus the remainder of the circuitry can be smaller with less propagation delay and the circuit is operated with less power dissipation.
The prior art programming circuitry is arranged such that the high current required for programming the memory is directed through all of the transistors of the circuitry, thus, the transistors have high current densities which reduces the speed of operation of the circuitry which is a factor of the current density and also require more power to operate. Additionally, the prior art decoder, if it is to be used also as a read circuitry after the programming of the memory, requires an additional current source, or alternatively two separate circuits; one for programming the memory and one for reading the memory.
Accordingly it is an object of this invention to increase the speed of the programming circuitry over the prior art circuitry and to direct the high current through a minimum number of components and thus operate the circuitry with smaller components, at higher speeds, and with less power consumption.